1. Field of the Invention
This invention relates to pressurized dispenser packages, such as aerosol packages, wherein the product to be dispensed and the pressure-generating media, i.e. the propellant, are maintained in isolation through separation on opposite sides of a barrier. An aerosol package of this type is generally referred to as a xe2x80x9cbarrier packxe2x80x9d aerosol package.
2. Description of the Prior Art
Aerosol barrier packs of the prior art have been of at least three general types. In the piston-type barrier pack the barrier is a piston-like component that is mounted in the container in sliding relation to the inside surface of the container. The product to be dispensed is disposed on the valved side of the piston and the propellant, which generates pressure within the container, is on the opposite side of the piston. In Aerosol Handbook, Second Edition, 1982, there is described a piston-type aerosol dispenser marketed by American Can Company under the tradename xe2x80x9cMira-Floxe2x80x9d. In the Mira-Flo dispenser the piston skirt is designed to seal against the sides of the container to prevent the propellant gas from passing into the product chamber on the other side of the piston. Actuation of the aerosol discharge valve causes a reduction in pressure in the product chamber thereby resulting in the pressure in the propellant chamber urging the piston toward the discharge valve and causing the discharge of product through the discharge valve. Examples of a piston-type barrier pack are described in U.S. Pat. Nos. 3,022,923, 3,756,476 and 3,929,132.
In a second type of aerosol barrier pack, a flexible, collapsible bag is affixed within the container opening either to the aerosol discharge valve or to the bead of the container opening. The Continental Can Company in the late 1960""s introduced an aerosol barrier dispenser known as the xe2x80x9cSepro-Canxe2x80x9d. The Sepro-Can includes an interior plastic product bag having an opening that is attached to the valve opening at the top of the container. The side walls of the bag extend along the side walls of the container and are pleated like an accordion so the bag can collapse inward and upward under the influence of pressure in the remainder of the container as the bag is emptied. Patents which illustrate a barrier pack of the second type are set forth in U.S. Pat. Nos. 3,788,521, 3,896,970 and 4,067,499. Modifications of barrier packs of the second type include attaching the bag to the side wall of the container or to the joint formed between the side wall of the container and the top of the container.
A third type of prior art barrier pack is an unfolding cup-shaped barrier wherein the barrier has an outer wall terminating in a sealing flange, said outer wall being disposed contiguous to the inner wall of the container. The inner wall of the barrier is initially folded within the outer wall, the inner wall terminating in an end closing portion. The barrier is contained in a valved aerosol container and sealed at the joint formed between the sidewall and the bottom end closure of the container. Product is admitted through the valved opening of the container and propellant through a port in the bottom end closure of the container. Actuation of the valve reduces the pressure in the product compartment and results in the inner wall of the barrier unfolding from within the outer wall of the barrier and causing the end-closing portion of the inner wall of the barrier to advance and thereby urge the product toward the discharge valve. A patent which illustrates the third type of prior art barrier pack is U.S. Pat. No. 3,109,463.
A problem with the piston-type barrier pack of the first type is the imperfect seal between the side skirt of the piston and the side wall of the container which allows propellant to seep into the product with consequent discharge of propellant during product discharge as well as contamination of the product with propellant. Also, it is not uncommon for aerosol containers to be dented and thus lose their true circumferential shape, with the consequence that the piston is incapable of axial movement within the container past the aberrant configuration.
A problem with barrier packs of the second type wherein the barrier is affixed to the valve or valve opening of the container is that the barrier collapses in a manner to cause pocketing of the product within the collapsible barrier with consequent undesirable diminution of the evacuation of the product from the container.
In the third type of prior art barrier pack described herein, the unfolding cup-shape barrier does not advance progressively and uniformly against the inner wall of the container but tends to pocket and entrap product against the wall or within pockets formed in the barrier itself as it unfolds. Attempts to solve these problems have included adding an additional rigid piston to the end-closing portion of the inner wall, or adhering the outer wall of the barrier in peelable fashion to the inner wall of the container. Generally, barriers of the third type can be difficult to form, as well as to insert into and seal with the container.
There is, therefore, a need for a flexible product/propellant barrier for an aerosol container that is easy to manufacture and ship, that is easy to insert into and seal to the container, that prevents leakage of the fluids from one compartment to the other compartment, and that does not pocket and therefore preclude evacuation of significant amounts of the product to be discharged.
The present invention relates to an improvement in the third type of barrier pack. In its broadest aspect, the present invention concerns a unitary flexible and expandable barrier for use in a plural-zoned, valved, pressure container wherein the barrier has a shaped spatial form having sufficient rigidity to maintain its shape prior to insertion into and use in a plural-zoned, valved pressure container. The barrier comprises a flexible and expandable wall portion having an outer wall segment and an inner wall segment connected by an angled fold, the free terminal end of the outer wall segment forming a sealing means and the terminus of the inner wall segment distal to the fold extending into a central piston region that closes the barrier. In a preferred form, the outer wall segment is steeply frustoconical in shape and terminates at its free end in a sealing means, and the inner wall segment is disposed in juxtaposed relation to the inner surface of the outer wall and in steeply frustoconical shape opposite to the frustoconical shape of the outer wall segment so as to form a small acute angle between the outer wall segment and the inner wall segment; the terminus of the inner wall segment distal to the fold being closed by a central piston region to thereby complete the unitary barrier member. Further, the inner wall segment is sufficiently flexible to permit the inner wall segment and said central piston region to move in an axially downward direction under the influence of product pressure when the barrier is top sealed within a container, to assume a more or less phallic configuration. Still further, the outer and inner wall segments have sufficient flexibility and expandability to extend outwardly under the influence of product pressure to substantially conform to the inner surface of the container. When the outer wall segment is sufficiently thicker and more rigid than the inner wall segment, the outer wall segment will tend to continue to substantially conform to the inner surface of the container, and the flexible inner wall segment will invert within the outer wall segment under the influence of propellant pressure to substantially return the barrier to approximately its shape as initially disposed in the container. Thereafter, the inner wall segment and central piston area will stretch radially outwardly and upwardly to substantially evacuate the product in the container. When the outer wall segment is less thick and less rigid, the inner wall segment and central piston will move axially upward under the influence of propellant pressure, followed by both the outer and inner wall segments crumpling tightly together and moving upward. In this latter instance, at least in the case of low viscosity products, product will be substantially evacuated from the container.
By virtue of having sufficient rigidity to maintain its shape prior to insertion into the container, as well as the presence of the tapered outer wall segment, the barrier of the present invention is very easily insertable into the top of the container. By virtue of the tapered outer and inner wall segments, the barrier is nestable with like barriers for convenience and cost savings in shipping. Further, the nesting facilitates fast and simple machine feeding of stacked barriers sequentially into the containers.
In a preferred form of the invention the outer wall segment is thicker and more rigid than the inner wall segment; the inner wall segment also is of slightly less length than the outer wall segment; and the sealing means is a radially extending flange which acts as a gasket between the top of the sidewall of the container and the top closure of the container. The central piston region also may be thicker than the inner wall segment.
A particularly advantageous material for barriers is polyethylene terephthalate (PET). Where permeation across the barrier is a concern, the barrier of the present invention may utilize a unitary multi-layer configuration. Such multi-layer configurations, their materials of construction and their manufacture, are well known to those skilled in the art. Generally, in a three-layer system, the inner layer is a material that prevents transport of propellant and product therethrough and the outer layers are inert to the propellant and product.